I have the same problem. Guy next to me does not. We swapped holsters and it did not help. Mine appears to be device related. Cingular said they would swap it out for a new one since it was within 30 days. I did a little testing and it works when I place the backside of the holster (magnet exposed side) on the blackberry keyboard. However, normal holster docking does not. If I press on the holster (around the magnet) while the device is holstered, the screen will shut off. Other way is to put it into the holster at an angle and scrape it across the magnet. This of course will eventually ruin the paint job. Which by the way, is black underneath the thin silver coat.

FOLLOW-UP***
Out of curiosity, I called RIM. They wanted me to reload the software. I declined on the grounds that it was a waste of my time. I am now calling Cingular back for my replacement.